Array comparisons compare the array contents
element-by-element, using the default B-Tree comparison function
for the element data type. In multidimensional arrays the
elements are visited in row-major order (last subscript varies
most rapidly). If the contents of two arrays are equal but the
dimensionality is different, the first difference in the
dimensionality information determines the sort order. (This is a
change from versions of PostgreSQL prior to 8.2: older versions
would claim that two arrays with the same contents were equal,
even if the number of dimensions or subscript ranges were
different.)